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ABSTRACT: The low‐pressure chemical‐vapor deposition of phosphorus‐doped silicon film on glass at 550 °C was investigated as a function of silane pressure (1–100 Pa) and phosphine/silane mole ratio ranging between 4×10<sup>-6</sup> and 4×10<sup>-4</sup>. At this low temperature the film is homogeneous in thickness and the silicon is amorphous except for low pressure (1 Pa). Phosphorus concentration varies linearly with mole ratio in amorphous deposited films. The resistivity of films annealed at 600 °C decreases while the incorporation of phosphorus (mole ratio) increases, and varies with phosphorus concentration from 10<sup>1</sup> to 10<sup>-3</sup> Ω cm. For the same phosphorus content, the resistivity is lower if the silicon film is amorphous deposited and subsequently crystallized, than if the film is polycrystalline deposited. Carrier concentration and mobility are measured using the Hall method. Doping efficiency and electrical properties are discussed.
Journal of Applied Physics 12/1994; · 2.17 Impact Factor
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ABSTRACT: Polysilicon devices on glass substrates for large-area
applications, such as poly-Si thin-film transistors in active-matrix
displays, need a complete low-temperature process, especially to
fabricate the drain and source polysilicon layers as well as the active
channel layer. For this purpose, we have developed a very low pressure
chemical vapour deposition process allowing in-situ phosphorous doping.
By varying total pressure and phosphine/silane ratio, we control the
doping concentration level over a large range (10<sup>18</sup> to
5×10<sup>20</sup> cm<sup>-3</sup>). Depending on deposition
conditions, films are first amorphous or partially crystallised. The
films are then fully crystallised by a 12 h in-situ vacuum annealing at
600°C. They are physically and electrically characterised. It is
observed that in the 30 to 90 pascal pressure range, the dopant
activation rate, electrical carrier mobility, and conductivity of the
layers are optimised whatever the doping level. First runs of low
temperature processed TFTs involving in-situ highly doped source and
drain layers have given promising results
IEE Proceedings - Circuits Devices and Systems 03/1994; · 0.36 Impact Factor
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ABSTRACT: The authors have developed a Very Low Pressure Chemical Vapor
Deposition process (VLPCVD) allowing in-situ phosphorous doping and have
tried both to control the doping level in a large range and to get a
related high conductivity. They show that controlling the deposition
parameters allows one to optimize the film conductivity, free carrier
mobility, and doping efficiency. This process has been used to fabricate
source and drain regions of thin film transistors
Poly-Si Devices and Applications, IEE Colloquium on; 04/1993
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ABSTRACT: Oxygen ionosorption, i.e. chemisorption that induces changes in the electrical conductivity, has been studied by resistivity and Spectroscopie (XPS and AES) measurements, on vacuum-deposited thin polycrystalline CdSe films. The results of electrical resistance variations during isothermal adsorptions (ΔR-IA), isothermal desorptions (ΔR-ID) and temperature programmed desorptions (ΔR-TPD) are analysed on samples prepared under various conditions. The influence of cadmium and selenium excess and of surface oxidation of the film on its oxygen adsorption capacity is shown. XPS and AES measurements made after similar adsorptions and desorptions prove the correlation between oxygen presence on the film surface and the behaviour of electrical resistance variations: reversible or irreversible.
Journal of Physics and Chemistry of Solids 53(5):723-732. · 1.63 Impact Factor
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ABSTRACT: A process giving a reproducible resistivity-temperature characteristic in vacuum is described. CdSe thin films were deposited under vacuum at various substrate temperatures TS and residual pressures PR. Their structural and electrical characteristics vary over a wide range. When the samples are deposited at PR > 1.33 mPa a surface excess of cadmium is present and revealed by thermal desorption and X-ray photoelectron spectroscopy (XPS). Vacuum (PR < 1.33 mPa) extended annealing releases part of this excess. Moreover, in every case a 2 h vacuum annealing at TA = 618 K considerably decreases the dispersion of the log ϱ(1/T) resistivity-temperature characteristics and makes them reproducible in vacuum at the residual annealing pressure provided that T < TA. Above T > 350 K, these characteristics are linear with slopes between 0.3 and 0.4 eV. XPS always reveals a relative cadmium excess and shows that foreign atoms (especially carbon and oxygen) are present only at the film surface.
Thin Solid Films 182:1-14. · 1.89 Impact Factor
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ABSTRACT: The aim of this study is to develop magnetic sensors (Hall generators) that can be realized on large area glass substrates and used as large position sensor. The magnetic sensor is constituted of particular polycrystalline silicon thin-film transistors that allows obtaining a significant Hall voltage induced by a magnetic field. The sensitivity of the magnetic cell, as well as the power dissipation depend on the gate and drain voltages. Two different structures with active layer lightly doped or undoped are studied. The highest measured sensitivity is about 20 mV/T with a low power dissipation (<2 mW).
Sensors and Actuators A: Physical.
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ABSTRACT: In order to obtain low in-situ phosphorus doped LPCVD polysilicon thin films having good conductivity, it is necessary to obtain an amorphous layer which is crystallized after deposition. This condition limits the choice of both temperature and pressure. An appropriate selection of deposition parameters has led to a phosphorus atom incorporation in the range 2 x 1018 - 2 x 1020 for a phosphine/silane mole ratio in the range 4 x 10-6 - 4 x 10-4. With these conditions, the resistivity varies from 1 to 2 x 10-3 [MATH]cm.
http://dx.doi.org/10.1051/jp4:1991296.
